The present invention relates to the technical field of data transmission. Devices connected to a data network, whether they are computers, computer workstations, or any other device capable of sending or receiving a signal are referred to as nodes in this description. In particular the present invention relates to data transmission between two nodes on a data network.
Data networks are used universally to transmit information between a very diverse range of computers, automated devices, control devices, telecommunications equipment, display systems and other devices.
It is common practice to have more than one physical connection between devices on a data network. A transmission fault in a network usually stops all traffic and hinders use of all devices connected to that network until the transmission fault has been located and fixed. As errors are so disruptive in industry and commercial organisations, a second physical network connection can be provided between points on a network. Such secondary network connections, where there exists a first network and a second network, either one of which may be redundant at some time, are also called redundant data networks. A computer connected to a data network may also be referred to as a host, as well as node. An application is a term used to describe a program that may run on a host computer or other device with processing capability. Thus an application may run on a host computer connected to a data network and such an application may communicate with other devices or applications running on other devices connected to that data network.
Conventional transmission standards, also called transport protocols, typically provide for an acknowledgement signal to be returned to a sending node on receipt of a message at the intended destination. In this way, the sending application or device is informed that the sent message arrived and no further action is required. If an acknowledgement signal is not received, then action is taken by the transmission protocol to re-transmit the last message.
Thus a known solution for error handling in a redundant data network is to transmit each message simultaneously via each separate route provided by redundant network connections between nodes. The receiving node, or a receiving application at a node discards second copies of any received message. This strategy ensures that a sent message is received almost 100% of the time. However, as half of the transmissions are duplicated messages, this results in a high traffic load to end nodes.
The object of the invention is to provide a method for handling transmissions without data loss in a redundant data network in a way that does not increase network traffic. A further object of the invention is that transmission errors be handled efficiently and sufficiently quickly. A still further object of the invention is to provide a method that does not require additional action by a message sender. An additional object of the invention is to provide a method which is compatible with contemporary transmission protocols.
These and other objects are achieved according to the invention by a data transmission method and device in a redundant data network as described in the claims. The present invention comprises a method and a device for handling transmissions in a redundant data network, in which at least two nodes are each connected to more than one network. The transmission method comprises the steps that after a message has been sent from one node to another, the time taken before a message acknowledgement is received at the sending node is measured, according to the known art. The present invention comprises that the message is resent to the destination via a second network when a timeout for receipt of the message acknowledgement expires. In an embodiment of the invention this is carried out by substituting a second network address in place of a first network address for the original destination before the retransmission takes place. Thus when a timeout occurs, the original message is automatically re-sent to the original destination via an alternate route over the redundant data network which is expressed as an alternate network address.
The main advantage of the present invention is that it handles transmission errors in a redundant data network without increasing node system load or network traffic. No data is lost, so the resulting redundant data network is fault tolerant. A further advantage of the present invention is that the method is completely invisible to a message sending device or application. This is a great technical advantage because it means that no modification is required to current hardware or to current computer applications. A still further advantage is that recovery from an transmission error may be chosen to take place very quickly, depending on network traffic requirements.
The time before retransmission may be selected in advance to be faster or slower in relation the existing level of network traffic. An additional further advantage of the invention is that a transmission error handling event is visible to a network controller, so that action to investigate or correct a fault can be initiated. As well as the above advantages, another advantage is that a method according to the invention is very useful as it may be used with any device or network that uses a standard transmission protocol.